get_activity: Get Fitbit activity data in a tidy format.
In Avsecz/fitbitr: An R Interface To The Fitbit API

Description Usage Arguments Details Value Feature description Examples

This function queries the Fitbit API and returns the activity data for different features in a tidy format.

1 2	get_activity(from_date, to_date = from_date, features = activity_features(), detail_level = "1min", token)

`from_date`	From which date to query the data. Character scalar in the format "YYYY-MM-DD".
`to_date`	Up to which date to query the data. Data for that day are included in the return value. Character scalar in the format "YYYY-MM-DD".
`features`	A character vector listing which features should be queried and included in the final data.table. Use `activity_features` to see all the available features.
`detail_level`	A character scalar specifying how frequently should the returned data be sampled. Possible options are: '15min', '1min' and '1sec'. Use `activity_features_info` to get minimal sampling time for each feature.
`token`	Fitbit API token generated with `get_fitbit_token`.

This is the main function of the fitbitr package. I queries the Fitbit API multiple times using the fitbit_GET function. It then parses the API outputs and combines them into a single data.table.

data.table with columns corresponding to different features as described in https://dev.fitbit.com/docs/activity/ and https://dev.fitbit.com/docs/heart-rate/. Each feature also contains the daily summary denoted with a daily_ prefix.

calories_level: Level field that reflects calculated activity level for that time period ( 0 - sedentary; 1 - lightly active; 2 - fairly active; 3 - very active.)
calories_mets: Probably the MET score https://help.fitbit.com/articles/en_US/Help_article/What-are-very-active-minutes.
calories: Calories burned in this time interval.
daily_calories: Total amount of calories burned at that day.
steps: Number of steps in this time interval.
daily_steps: Total number of steps at that day.
distance: Distance made in this time interval.
daily_distance: Total distance made at that day.
floors: Number of floors made in this time interval.
daily_floors: Number of floors made in this time interval.
elevation: Elevation units made in this time interval.
daily_elevation: Total number of elevation units made at that day.
heart: Mean heart rate in this time interval [beats per second].
daily_elevation: Daily mean heart rate [beats per second].

Currently used units are 'Metric' (described in https://dev.fitbit.com/docs/basics/#unit-systems).

Time and date are stored as character vectors.

## Not run: 
fitbit_token <- get_fitbit_token()
dt <- get_activity(from_date = "2015-12-15", to_date = "2015-12-18", token = fitbit_token)

## Heart rate at 1 second precision for the day 2015-12-15
dt <- get_activity(from_date = "2015-12-15", features = "heart",
                   detail_level = "1sec",
                   token = fitbit_token)

## End(Not run)